Air chamber polarization enhanced magnetometer based on multifocal holographic metasurface and measuring method

Abstract

The application discloses a kind of gas chamber polarization enhancement magnetometer based on multifocal holographic super surface and measuring method, belong to magnetic field measurement technical field.The magnetometer includes laser generation and control module, 1 / 4 wave plate, multifocal holographic super surface, optical magnetic resonance module, optical pumping signal post-processing module and reflector.Laser is collimated after 1 / 4 wave plate and is incident to multifocal holographic super surface, the super surface carries out phase control to incident light, makes multiple focal planes in different depths in gas chamber, improves the spatial uniformity of light pumping, enhances alkali atom polarization rate.Transmitted light enters optical pumping signal post-processing module, passes through polarizing beam splitter prism polarizing beam splitter prism, balanced differential detector and lock-in amplifier, extracts magnetic resonance signal and calculates magnetic field intensity.The application optimizes light pumping process, improves the stability and signal-to-noise ratio of magnetic measurement system, reduces measurement error, and is suitable for geomagnetic detection, biological magnetic signal detection and other high-sensitivity magnetic field measurement fields.

Description

Technical Field

[0001] This invention belongs to the field of magnetic field measurement technology, and particularly relates to a gas-cell polarization-enhanced magnetometer and measurement method based on a multifocal holographic metasurface. Background Technology

[0002] Magnetic fields are important physical quantities generated by moving electric charges, and they have a wide-ranging impact on the natural environment, industrial applications, and life sciences. Magnetic field measurement technology has become an important research direction in fields such as fundamental physics, geophysics, biomedicine, and military defense. Among these, high-precision magnetic measurement equipment is crucial for applications such as magnetic anomaly detection, resource exploration, and life and health monitoring.

[0003] Atomic magnetometers currently hold the record for the highest magnetic field measurement sensitivity, showing broad application prospects in geophysical exploration, deep space exploration, and biomagnetic imaging. With the development of small UAV-borne magnetometers and portable health monitoring devices, atomic magnetometers are gradually being implemented on chips. However, existing optically pumped magnetometer technology still faces the following key bottlenecks:

[0004] ① Non-uniformity of optical pumping: Traditional optical pumping relies on the free propagation of laser light. As the laser penetrates deeper into the gas cell, the optical power gradually decreases, resulting in non-uniform polarization distribution of alkali metal atoms in the gas cell, which affects the quality of magnetic resonance signal.

[0005] ②Limited polarizability: Existing optical systems cannot efficiently utilize pump light, resulting in insufficient polarizability of alkali metal atoms, which limits the sensitivity of the magnetometer.

[0006] ③ System integration issues: Existing systems typically use lens or fiber coupling schemes to control lasers, resulting in large device sizes that are not conducive to portable applications.

[0007] To address the aforementioned issues, this paper proposes a cell-based polarization-enhanced magnetometer based on a multi-focal-plane holographic metasurface. This method utilizes specially designed metasurface optical elements to create multiple focal planes at the rear end of the cell, achieving a more uniform optical pump distribution. This improves the polarization uniformity of alkali metal atoms, increases the optical pump rate, and enhances the sensitivity and stability of the magnetic measurement system. Compared to traditional methods, this approach offers higher integration and stability, providing a novel solution for portable, high-precision magnetic measurements. Summary of the Invention

[0008] This invention provides a gas-cell polarization-enhanced magnetometer and measurement method based on a multifocal holographic metasurface. By introducing multifocal holographic metasurface technology, leveraging its lightweight, two-dimensional integration, and multifunctional characteristics, and utilizing submicron-level structures to precisely control light propagation characteristics, the light field distribution of the laser within the gas cell becomes more uniform, achieving efficient polarization enhancement. This, in turn, improves the sensitivity and stability of the magnetic measurement system, making the overall structure meet the design requirements of miniaturization, high sensitivity, and high integration.

[0009] The technical solution of the present invention is as follows:

[0010] A gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface is characterized by comprising a laser generation and control module, a quarter-wave plate, a multifocal holographic metasurface, an optical magnetic resonance module, and an optical pump signal post-processing module connected in sequence. The multifocal holographic metasurface spatially phase-modulates the circularly polarized light from the quarter-wave plate and forms multiple focal planes at different depths along the beam propagation direction within the alkali metal gas cell of the optical magnetic resonance module, thereby reducing the polarization gradient caused by uneven light intensity distribution within the gas cell.

[0011] The spatial phase modulation of the multifocal holographic metasurface includes using the principle of holographic lenses to divide the incident laser into multiple depth layers along the beam propagation direction, and using a single metasurface to integrate and encode the phase information of multiple holographic lenses to achieve precise phase modulation at the subwavelength level.

[0012] The laser generation and control module includes a laser and a laser controller, and the laser is connected to the laser controller and the quarter-wave plate respectively.

[0013] The optical magnetic resonance module includes an oven in which the alkali metal gas chamber is placed. An electric heating wire and a radio frequency coil are provided between the oven and the alkali metal gas chamber. The electric heating wire is connected to the oven temperature control system.

[0014] The optical pump signal post-processing module includes a polarizing beam splitter, a balanced differential detector, a lock-in amplifier, and a reflector. The input side of the polarizing beam splitter is connected to the laser emission side of the alkali metal gas cell, the transmission side of the polarizing beam splitter is connected to the first input terminal of the balanced differential detector, the reflection side of the polarizing beam splitter is connected to the second input terminal of the balanced differential detector through the reflector, and the output terminal of the balanced differential detector is connected to the lock-in amplifier.

[0015] A measurement method for a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface, characterized by comprising the following steps:

[0016] Step 1, Laser frequency tuning and locking: Adjust the laser's operating parameters through the laser controller to match the laser wavelength with the resonant transition frequency of alkali metal atoms, ensuring the stability of the optical pumping process and improving polarizability;

[0017] Step 2, Alkali Metal Chamber Temperature Monitoring and Control: Set the target heating temperature and PID control parameters for the oven. The oven temperature control system measures the internal temperature of the oven through a thermistor, calculates the deviation between the target temperature and the actual temperature, and adjusts the power output of the electric heating wire according to the PID to keep the oven temperature stable, ensuring that the evaporation of alkali metal atoms in the chamber reaches a steady state and improving the signal-to-noise ratio of the magnetic resonance signal.

[0018] Step 3, Optical Pumping and Detection: The laser sequentially passes through a quarter-wave plate and a multi-focal-surface holographic metasurface. The multi-focal-surface holographic metasurface performs phase modulation on the incident light, causing it to form multiple focal planes at different depths within the alkali metal gas cell, thus improving the uniformity of optical pumping. The modulated laser enters the alkali metal gas cell at a fixed angle, causing the alkali metal atoms within the gas cell to be uniformly polarized. The polarized atoms interact with the external magnetic field, resulting in a change in the optical signal during transmission. The transmitted light then enters the optical pump signal post-processing module.

[0019] Step 4, Magnetic Field Signal Processing and Calculation: The optical pump signal post-processing module includes a polarizing beam splitter, a photodetector, and a lock-in amplifier, used to extract the magnetic resonance signal and calculate the external magnetic field strength. After the emitted laser enters the optical pump signal post-processing module, it is split by the polarizing beam splitter and then enters the photodetector, where it is converted into an electrical signal and processed. The lock-in amplifier modulates the radio frequency signal and applies it to the radio frequency coil, scanning the magnetic resonance signal within a set frequency range to obtain the Larmor precession frequency and calculate the external magnetic field strength.

[0020] The technical effects of this invention are as follows: This invention provides a gas-cell polarization-enhanced magnetometer and measurement method based on a multi-focal-plane holographic metasurface. It employs a light field modulation scheme based on a multi-focal-plane holographic metasurface. Building upon a single-beam magnetometer, it uses the principle of holographic lenses to divide the incident laser beam into multiple depth layers along the beam propagation direction. A single metasurface integrates and encodes the phase information of multiple holographic lenses, achieving precise phase modulation at the subwavelength level. Consequently, the light field forms multiple precisely positioned focal planes within the gas cell, achieving uniform focusing of laser energy, significantly improving the polarizability and polarization uniformity of alkali metal atoms, thereby enhancing the amplitude and signal-to-noise ratio of the magnetic resonance signal and greatly improving the sensitivity and stability of magnetic field measurements.

[0021] Furthermore, by effectively reducing the polarization gradient caused by uneven light intensity distribution, the present invention reduces signal distortion caused by local over-pumping or under-polarization, significantly improving the accuracy and repeatability of measurements. Compared to traditional optical pumping methods, this scheme can improve the utilization efficiency of pump light in the gas cell and reduce the polarization gradient problem caused by uneven light intensity distribution, thereby improving the stability and repeatability of magnetic field measurements. Higher polarization within the gas cell enhances the magnetic resonance signal amplitude and improves the signal-to-noise ratio of the magnetometer, while a more uniform polarization distribution reduces signal distortion caused by local under-polarization or over-pumping, making magnetic field measurements more accurate and reliable, further reducing systematic errors, and improving the sensitivity of magnetic field measurements. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface according to the present invention.

[0023] Figure 2 yes Figure 1 A schematic diagram illustrating the principle of forming multifocal surfaces in an alkali metal gas cell using a multifocal holographic metasurface.

[0024] The following are the annotations in the attached figures: 1-Laser generation and control module; 2-Laser; 3-Laser controller; 4-1 / 4 wave plate; 5-Multi-focal-plane holographic metasurface; 6-Optical magnetic resonance module; 7-Oven; 8-Electrically heating wire; 9-Alkali metal gas chamber; 10-RF coil; 11-Oven temperature control system; 12-Optical pump signal post-processing module; 13-Polarizing beam splitter prism; 14-Balanced differential detector; 15-Lock-in amplifier; 16-Mirror; 17-Circularly polarized light; 18-First focal plane (i.e., front focusing plane); 19-Second focal plane (i.e., middle focusing plane); 20-Third focal plane (i.e., rear focusing plane); 21-Polarized atom. Detailed Implementation

[0025] The following is in conjunction with the attached diagram ( Figures 1-2 The invention will be described in the following sections and examples.

[0026] Figure 1 This is a schematic diagram of a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface according to the present invention. Figure 2 yes Figure 1 A schematic diagram illustrating the principle of multifocal surface formation in an alkali metal gas cell using a mid-focal surface holographic metasurface. (Reference) Figures 1 to 2As shown, a cell-based polarization-enhanced magnetometer based on a multifocal holographic metasurface includes a laser generation and control module 1, a quarter-wave plate 4, a multifocal holographic metasurface 5, an optical magnetic resonance module 6, and an optical pump signal post-processing module 12 connected in sequence. The multifocal holographic metasurface 5 spatially phase-modulates the circularly polarized light 17 from the quarter-wave plate 4 and forms multiple focal planes at different depths along the beam propagation direction within the alkali metal cell 9 in the optical magnetic resonance module 6 (for example, the first focal plane 18 is the front focusing plane, the second focal plane 19 is the middle focusing plane, and the third focal plane 20 is the rear focusing plane; alkali metal atoms in the cell become polarized atoms 21 under the action of the light field formed by the multiple focal planes), thereby reducing the polarization gradient caused by the uneven distribution of light intensity in the cell. The spatial phase modulation of the multifocal holographic metasurface 5 includes using the principle of holographic lenses to divide the incident laser into multiple depth layers along the beam propagation direction, and using a single metasurface to integrate and encode the phase information of multiple holographic lenses to achieve precise phase modulation at the subwavelength level.

[0027] The laser generation and control module 1 includes a laser 2 and a laser controller 3. The laser 2 is connected to the laser controller 3 and the quarter-wave plate 4. The optical magnetic resonance module 6 includes an oven 7 in which the alkali metal gas chamber 9 is built. An electric heating wire 8 and an RF coil 10 are arranged between the oven 7 and the alkali metal gas chamber 9. The electric heating wire 8 is connected to the oven temperature control system 11. The optical pump signal post-processing module 12 includes a polarizing beam splitter 13, a balanced differential detector 14, a lock-in amplifier 15, and a reflector 16. The input side of the polarizing beam splitter 13 is connected to the laser emission side of the alkali metal gas chamber 9. The transmission side of the polarizing beam splitter 13 is connected to the first input terminal of the balanced differential detector 14. The reflection side of the polarizing beam splitter 13 is connected to the second input terminal of the balanced differential detector 14 through the reflector 16. The output terminal of the balanced differential detector 14 is connected to the lock-in amplifier 15.

[0028] This invention discloses a gas-cell polarization-enhanced magnetometer and measurement method based on a multifocal holographic metasurface, belonging to the field of magnetic field measurement technology. The magnetometer includes a laser generation and control module, a quarter-wave plate, a multifocal holographic metasurface, an optical magnetic resonance module, an optical pump signal post-processing module, and a reflector. The laser beam, collimated by the quarter-wave plate, is incident on the multifocal holographic metasurface. The metasurface performs phase modulation on the incident light, causing the light field to form multiple focal planes at different depths within the gas cell, improving the spatial uniformity of optical pumping and enhancing the polarizability of alkali metal atoms. The transmitted light enters the optical pump signal post-processing module, passes through a polarization beam splitter, a balanced differential detector, and a lock-in amplifier, and extracts the magnetic resonance signal to calculate the magnetic field strength. This invention optimizes the optical pumping process, improves the stability and signal-to-noise ratio of the magnetic measurement system, and reduces measurement errors, making it suitable for high-sensitivity magnetic field measurement fields such as geomagnetic detection and biomagnetic signal detection.

[0029] A gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface includes: a laser generation and control module, a quarter-wave plate, a multifocal holographic metasurface, an optical magnetic resonance module, an optical pump signal post-processing module, and a reflector;

[0030] The laser generation and control module includes a laser and a laser controller. The laser controller adjusts the laser to ensure a stable output of laser light with a specific wavelength and power.

[0031] The quarter-wave plate is used to adjust the divergence angle of the laser, making its beam characteristics suitable for phase modulation on a multifocal holographic metasurface.

[0032] The multifocal holographic metasurface utilizes a precisely designed submicron structure to spatially control the phase of incident laser light. Utilizing the principle of geometric phase, by adjusting the size, shape, period, and rotation angle of the nanostructure, the phase information of multiple holographic lenses is integrated onto a single metasurface. This allows the laser to form multiple precise focal planes at different depths within the alkali metal gas chamber, thereby optimizing light pump uniformity and improving atomic polarizability.

[0033] The optical magnetic resonance module includes an alkali metal gas cell, where polarized atoms undergo Larmor precession under the influence of an external magnetic field, affecting the polarization state of the transmitted light.

[0034] The transmitted light enters the optical pump signal post-processing module, which receives the signal and generates a radio frequency magnetic field to the driving optical magnetic resonance module to obtain the Larmor precession frequency and calculate the magnetic field strength.

[0035] The operating parameters of the laser generation and control module include the laser's operating temperature, operating current, and output wavelength, to ensure that the pump light matches the resonant transition frequency of the alkali metal atoms.

[0036] The multifocal holographic metasurface precisely modulates the phase of incident light through periodic nanostructures, forming multiple focal planes at different depths in the alkali metal gas cell. This improves the uniformity of light pumping, enhances the atomic polarization process, and reduces the influence of polarization gradients on the magnetic measurement signal.

[0037] The optical magnetic resonance module includes: an alkali metal gas chamber, an oven, an oven temperature control system, a radio frequency coil frame, and a radio frequency coil;

[0038] The alkali metal gas chamber is filled with alkali metal atomic gas and buffer gas, and has a window to allow laser transmission.

[0039] The oven: encloses the alkali metal gas chamber and provides a stable heating environment to maintain the evaporation state of the alkali metal atoms;

[0040] The oven temperature control system uses electric heating wires and thermistors to achieve temperature monitoring and feedback control, so as to maintain the internal temperature of the alkali metal chamber and improve the stability of the photo-pumping process.

[0041] The radio frequency coil is fixed on the radio frequency coil support frame and driven by a lock-in amplifier to provide an alternating magnetic field to excite atoms to undergo Larmor precession.

[0042] The oven temperature control system adopts a PID control strategy (PID stands for proportional-integral-derivative) to adjust the heating power in real time according to the measured internal temperature of the oven, so as to reduce the impact of temperature fluctuations on the magnetic measurement signal.

[0043] The optical pump signal post-processing module includes: a polarizing beam splitter, a balanced differential detector, and a lock-in amplifier.

[0044] The polarizing beam splitter splits the transmitted light into two mutually perpendicular beams. One beam propagates along the original direction, while the other beam, after its optical path is adjusted by a reflector, becomes parallel to the first beam and is simultaneously incident into a balanced differential detector for light intensity detection.

[0045] The balanced differential detector performs differential processing on the two optical signals to improve the signal-to-noise ratio and reduce the impact of light intensity fluctuations on the measurement results.

[0046] The lock-in amplifier amplifies and filters the output signal of the balanced differential detector and applies radio frequency scanning to extract the characteristic frequency of the magnetic resonance signal and calculate the magnetic field strength.

[0047] The frequency range of the radio frequency magnetic field generated by the radio frequency coil is adjustable and connected to a lock-in amplifier, enabling the system to perform magnetic resonance signal measurement under different magnetic field environments and adapt to the measurement requirements of different magnetic field strengths.

[0048] A measurement method for a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface includes:

[0049] Step 1: Laser frequency tuning and locking;

[0050] By adjusting the laser's operating parameters using a laser controller, the laser wavelength is matched to the resonant transition frequency of alkali metal atoms, ensuring the stability of the optical pumping process and improving polarizability.

[0051] Step 2: Temperature monitoring and control of the alkali metal gas chamber;

[0052] The target heating temperature and PID control parameters of the oven are set. The oven temperature control system measures the internal temperature of the oven through a thermistor, calculates the deviation between the target temperature and the actual temperature, and adjusts the power output of the electric heating wire according to the PID to keep the oven temperature stable, ensure that the evaporation of alkali metal atoms in the chamber reaches a steady state, and improve the signal-to-noise ratio of the magnetic resonance signal.

[0053] Step 3: Optical pumping and detection;

[0054] The laser beam sequentially passes through a quarter-wave plate and a multifocal holographic metasurface. The multifocal holographic metasurface performs phase modulation on the incident light, causing it to form multiple focal planes at different depths within the alkali metal gas cell, thus improving the uniformity of light pumping. The modulated laser beam enters the alkali metal gas cell at a fixed angle, causing the alkali metal atoms within the gas cell to become uniformly polarized. The polarized atoms interact with the external magnetic field, resulting in a change in the optical signal during transmission. The transmitted light then enters the optical pump signal post-processing module.

[0055] Step 4: Magnetic field signal processing and calculation;

[0056] The optical pump signal post-processing module includes a polarizing beam splitter, a photodetector, and a lock-in amplifier, used to extract the magnetic resonance signal and calculate the external magnetic field strength. After the emitted laser enters the optical pump signal post-processing module, it is split by the polarizing beam splitter and then enters the photodetector, where it is converted into an electrical signal and processed. The lock-in amplifier modulates the radio frequency signal and applies it to the radio frequency coil, scanning the magnetic resonance signal within a set frequency range to obtain the Larmor precession frequency and calculate the external magnetic field strength.

[0057] refer to Figure 1 As shown, a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface includes: a laser generation and control module 1, a quarter-wave plate 4, a multifocal holographic metasurface 5, an optical magnetic resonance module 6, an optical pump signal post-processing module 12, and a reflector 16. The laser generation and control module 1 generates a stable pump light, which passes sequentially through the quarter-wave plate 4 and the multifocal holographic metasurface 5 along the optical path. The multifocal holographic metasurface 5 performs spatial phase modulation on the incident beam, causing it to form multiple focal planes inside the gas cell, thereby improving the uniformity of the optical field and optimizing the atomic polarizability. The laser light after being processed by the optical magnetic resonance module 6 enters the optical pump signal post-processing module 12, which receives and processes the transmitted light signal to extract the magnetic resonance signal and calculate the Larmor precession frequency corresponding to the magnetic field strength.

[0058] As an example, the laser generation and control module 1 includes a laser controller 3 and a laser 2. The laser controller 3 controls the frequency, power, and temperature of the laser 2 to ensure laser stability and to guarantee the matching of the pump light with the resonant transitions of alkali metal atoms. As a preferred example, the quarter-wave plate 4 is used to adjust the polarization state of the laser, so that the beam incident on the multi-focal-plane holographic metasurface 5 is circularly polarized, improving the metasurface's efficiency in controlling the light field and avoiding the polarization process being affected by the beam deviating from the focal plane.

[0059] As an example, the optical magnetic resonance module 6 includes: an oven 7, an electric heating wire 8, an alkali metal gas chamber 9, a radio frequency coil 10, and an oven temperature control system 11. The oven 7 houses the alkali metal gas chamber 9 and provides heat through the electric heating wire 8 to regulate the chamber temperature, maintaining and stabilizing the appropriate vapor pressure of alkali metal atoms and ensuring the stability and density uniformity of the atomic vapor within the chamber. The alkali metal gas chamber 9 contains alkali metal atomic vapor and buffer gas, through which the laser beam penetrates to achieve optical pump polarization. The radio frequency coil 10 is arranged around the alkali metal gas chamber 9. When the radio frequency field frequency and the Larmor precession frequency of the alkali metal atoms are the same, optical magnetic resonance occurs, and this signal is transmitted to a lock-in amplifier 15. The oven temperature control system 11, through feedback control via the electric heating wire 8 and a temperature sensor, achieves precise adjustment of the internal temperature of the oven 7 to improve the quality of the magnetic resonance signal.

[0060] As an example of application, the multifocal holographic metasurface 5 is composed of multiple periodically arranged subwavelength nanostructures. These nanostructures are typically cuboid or cylindrical in shape and can be designed based on various control mechanisms such as geometric phase, resonant phase, or propagation phase. By precisely controlling the size, shape, orientation angle, and periodic arrangement of the nanostructures, the phase information of multiple holographic lenses with different focal lengths is superimposed on the same metasurface, allowing the incident light to form multiple independent focal planes at different longitudinal depths. This not only compensates for the gradual attenuation of optical power within the gas chamber but also enhances the optical field effect in the deeper regions of the gas chamber, thereby enabling alkali metal atoms to obtain a more uniform polarization state throughout the entire gas chamber, significantly improving the amplitude and consistency of the magnetic resonance signal.

[0061] As an example, the optical pump signal post-processing module 12 includes: a polarizing beam splitter 13, a balanced differential detector 14, and a lock-in amplifier 15. The polarizing beam splitter 13 splits the transmitted light according to its polarization state, causing one beam to propagate along its original direction while the other beam is deflected and enters the balanced differential detector 14, thereby improving signal extraction accuracy. The balanced differential detector 14 performs differential detection on the two light signals, effectively suppressing light source fluctuations and background noise, and improving the signal-to-noise ratio. The lock-in amplifier 15 amplifies and filters the differential signal output from the balanced differential detector 14, and extracts the magnetic resonance signal using a lock-in amplification method to calculate the Larmor precession frequency and thus estimate the external magnetic field strength.

[0062] As an example, the multi-focal-plane holographic metasurface 5, through precise optical field manipulation, makes light pumping more uniform, effectively improving the stability and sensitivity of the magnetic resonance signal. This scheme reduces the inhomogeneity of the light field during propagation, making the response of the magnetic resonance signal more stable and improving the system's anti-interference capability and measurement accuracy. Furthermore, this design has high integration, occupies little space, simplifies the optical system, reduces the size and complexity of traditional lens systems, and contributes to the miniaturization of high-precision magnetic field measurement equipment, providing a better solution for portable and integrated magnetic measurement systems.

[0063] Reference Figure 1 As shown, the operating temperature and driving current of the laser 2 are set by the laser controller 3 to stabilize the wavelength of the output laser near the D1 transition line of the Rb atom (794.979nm), and the laser power is adjusted to an appropriate level to ensure that the pump light effectively acts on the alkali metal atoms in the gas chamber and achieves polarization, while avoiding nonlinear effects that may be caused by excessive light intensity.

[0064] In the experimental environment, the target temperature of the oven 7 is set to 80-120℃ by the oven temperature control system 11. The oven temperature control system monitors the real-time temperature inside the oven through the built-in thermistor and dynamically adjusts the output power of the electric heating wire 8 using the PID control strategy to ensure that the alkali metal atoms in the alkali metal gas chamber 9 evaporate to a stable vapor density, thereby improving the stability and repeatability of the magnetic resonance signal.

[0065] The laser beam emitted by laser 2 passes sequentially through a quarter-wave plate 4 and a multifocal holographic metasurface 5. The quarter-wave plate 4 achieves polarization conversion of the beam, reducing beam divergence; the multifocal holographic metasurface 5 spatially modulates the phase of the incident beam, forming multiple focal planes at different depths within the alkali metal gas chamber 9. For example... Figure 2As shown, the alkali metal gas chamber 9 has an inner length of 8 mm. Holographic multifocal surfaces are fixed at a distance of about 4 mm from the alkali metal gas chamber 9, with focal lengths of 5 mm, 8 mm, and 11 mm, forming three focal surfaces. This achieves more uniform light pumping throughout the gas chamber, improves the uniformity of alkali metal atom polarization, and reduces signal distortion caused by uneven polarization.

[0066] Polarized atoms undergo Larmor precession under the influence of an external magnetic field, generating photomagnetic resonance and causing changes in the intensity of transmitted light. The transmitted light enters the optical pump signal post-processing module 12, where it is split into two beams by the polarization beam splitter 13. One beam propagates along its original direction, while the other beam, after being oriented by the reflector 16, becomes parallel to the first beam and enters the balanced differential detector 14 together. The balanced differential detector 14 performs differential calculations on the intensity signals of the two beams to effectively suppress noise, enhance signal contrast, and improve detection sensitivity.

[0067] The lock-in amplifier 15 applies an AC radio frequency signal to the radio frequency coil 10 within a certain frequency range and scans the differential change of the light intensity signal received from the balanced differential detector 14. When the amplitude of the detected magnetic resonance signal reaches its extreme value, the corresponding radio frequency is the Larmor precession frequency ω, and the strength of the magnetic field to be measured can be calculated using the following formula:

[0068] ω=γB0

[0069] Where γ = 7 Hz / nT is the gyromagnetic ratio of rubidium atoms, and B0 is the external magnetic field strength.

[0070] Based on the radio frequency ω corresponding to the peak value of the measured magnetic resonance signal, the external magnetic field strength B0 can be calculated using the above formula, and the measurement accuracy can be improved by combining multiple measurement results. Compared with traditional optically pumped magnetometers, this invention utilizes a multi-focal-plane holographic metasurface to improve the spatial uniformity of optical pumping, thereby enhancing the signal stability, sensitivity, and anti-interference capability of the magnetic measurement system. It is suitable for high-precision magnetic field measurement applications such as geomagnetic measurement and biomagnetic field detection.

[0071] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0072] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

[0073] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0074] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0075] In the embodiments provided in this application, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, devices, or units, and may be electrical, mechanical, or other forms.

[0076] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0077] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0078] The above description is only a preferred embodiment of the present invention. It should be understood that the above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention, and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, etc. made within the idea and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface, characterized in that, The system includes a laser generation and control module, a quarter-wave plate, a multi-focal-plane holographic metasurface, an optical magnetic resonance module, and an optical pump signal post-processing module, which are connected in sequence. The multi-focal-plane holographic metasurface spatially modulates the circularly polarized light from the quarter-wave plate and forms multiple focal planes at different depths along the beam propagation direction in the alkali metal gas chamber of the optical magnetic resonance module, thereby reducing the polarization gradient caused by uneven light intensity distribution in the gas chamber. The spatial phase control of the multifocal holographic metasurface includes using the principle of holographic lenses to divide the incident laser into multiple depth layers along the beam propagation direction, and using a single metasurface to integrate and encode the phase information of multiple holographic lenses to achieve precise phase control at the subwavelength level. The optical magnetic resonance module includes an oven in which the alkali metal gas chamber is placed. An electric heating wire and a radio frequency coil are provided between the oven and the alkali metal gas chamber. The electric heating wire is connected to the oven temperature control system. The optical pump signal post-processing module includes a polarizing beam splitter, a balanced differential detector, a lock-in amplifier, and a reflector. The input side of the polarizing beam splitter is connected to the laser emission side of the alkali metal gas cell, the transmission side of the polarizing beam splitter is connected to the first input terminal of the balanced differential detector, the reflection side of the polarizing beam splitter is connected to the second input terminal of the balanced differential detector through the reflector, and the output terminal of the balanced differential detector is connected to the lock-in amplifier.

2. The gas-cell polarization-enhanced magnetometer based on a multi-focal-plane holographic metasurface according to claim 1, characterized in that, The laser generation and control module includes a laser and a laser controller, and the laser is connected to the laser controller and the quarter-wave plate respectively.

3. A measurement method for a gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface, characterized in that, The gas-cell polarization-enhanced magnetometer based on a multifocal holographic metasurface as described in any one of claims 1-2 includes the following steps: Step 1, Laser frequency tuning and locking: Adjust the laser's operating parameters through the laser controller to match the laser wavelength with the resonant transition frequency of alkali metal atoms, ensuring the stability of the optical pumping process and improving polarizability; Step 2, Alkali Metal Chamber Temperature Monitoring and Control: Set the target heating temperature and PID control parameters for the oven. The oven temperature control system measures the internal temperature of the oven through a thermistor, calculates the deviation between the target temperature and the actual temperature, and adjusts the power output of the electric heating wire according to the PID to keep the oven temperature stable, ensuring that the evaporation of alkali metal atoms in the chamber reaches a steady state and improving the signal-to-noise ratio of the magnetic resonance signal. Step 3, Optical Pumping and Detection: The laser sequentially passes through a quarter-wave plate and a multi-focal-surface holographic metasurface. The multi-focal-surface holographic metasurface performs phase modulation on the incident light, causing it to form multiple focal planes at different depths in the alkali metal gas cell, thus improving the uniformity of optical pumping. The modulated laser enters the alkali metal gas cell at a fixed angle, causing the alkali metal atoms in the gas cell to be uniformly polarized. The polarized atoms interact with the external magnetic field, causing the optical signal to change during transmission. The transmitted light then enters the optical pump signal post-processing module. Step 4, Magnetic Field Signal Processing and Calculation: The optical pump signal post-processing module includes a polarizing beam splitter, a photodetector, and a lock-in amplifier, used to extract the magnetic resonance signal and calculate the external magnetic field strength. After the emitted laser enters the optical pump signal post-processing module, it is split by the polarizing beam splitter and enters the photodetector separately. It is converted into an electrical signal and processed. The lock-in amplifier modulates the radio frequency signal and applies it to the radio frequency coil. The magnetic resonance signal is scanned within a set frequency range to obtain the Larmor precession frequency and calculate the external magnetic field strength.

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